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on the river and its branches was about 200; and that number has probably since been nearly doubled. " Economy," says Mr. Stevens on in his Engineering Tour, " would seem to be the only object which the coustructors of these boats have in view; and therefore, with the exception of the finery which the cabins generally display, little care is expended in their construction, and much'of the workmanship connected with them is of a most imperfect and insufficient kind. When the crews of these frail fabrics, therefore, engage in brisk competition with other ve els, and urge the machinery to the utmost extent of its power, it is not to be wondered at that their exertions are often suddenly terminated by the ve el taking fire and going to the bottom, or by an explosion of the steam boilers. Such accidents are frequently attended with an appalling lo of life, and are of so common occurrence that they generally excite little or no attention." The steamers of the Mi i ippi vary in magnitude from 100 to 700 tons; and, unlike the light mould of the Hudson steamers, they are heavily built, so as to give them abundant tonnage for goods. They are built with a flat bottom, with a draught of from 6 to 8 feet of water, A deck is supported by the hull at about 5 feet above the level of the water, and the space in the hull under this deck is appropriated to the cargo. The whole of the steam machinery is placed on this deck; the engine standing in the middle of the ve el, and the boilers and furnaces towards the bow. That part of the lower deck towards the stern is occupied by the crew and deck pa engers, and is generally a scene of great filth and squalor. From the front of the paddle boxes, a staircase leads to a gallery or balcony of about 3 feet in width, which surrounds a structure raised upon the deck, and extending nearly the whole length of the ve el, presenting the external appearance of a long wooden house, the doors and windows of which open on this balcony. This structure is, in fact, the great cabin, extending from the two smoke funnels to within about 30 feet of the stern; this latter space, extending quite to the stern, is appropriated to the ladies' cabin. The large cabin, which contains the gentlemen's berths, is also used as the chief dining room. From the balcony just mentioned staircases on either side lead to the third, or upper deck, 30 feet above the level of the water. The wheel house, in which the steersman is placed, is erected on the fore part of this deck, and the motion is communicated to the helm by ropes or iron rods. The engines are constructed with very small cylinders, worked with steam of great pre ure. The diameter of the cylinder is often under 18 inches, while the length of stroke is from 5 to 6 feet. The safety valve is usually loaded with 100 lbs. per square inch, which, at the discretion of the captain, is sometimes increased to 1.50 lbs. Some of the large boats on the Mi i ippi are equal in magnitude to those on the Hudson, having a length of 230 feet, and a breadth of beam of 28 feet. With this great magnitude of deck and a capacity of not le than 1000 tons, they do not draw above 8 feet of water. For further details respecting steam navigation in general, and in the United States, see Dr. Lardncr on the Steam Engine, 7th edition; Appendix to Tredgold on the Steam Engine; and Stevens on's Civil Engineering in North America. STEA'RIC ACID. (Gr. Page 1184